I have a metal yardstick that I use to use when I did woodworking. I drilled small holes at each 1", 1/2" and 1/4" so when I need to draw a circle I can do the same as most of the ours here say. The only thing is, I started my holes at the 1" mark and use that as the center point then use a long push pin to hold it down. I have to add 1" to the size I need but it works great.
Your could always get a smaller 2' ruler and do the same thing.